1. Technical Field of the Invention
This patent relates to balancing machines in general, and in particular to balancing machines for motor vehicle wheels.
2. Prior Art
These machines comprise a rotary shaft supported at two points by a generally tubular frame fixed to a very rigid bed.
The shaft is connected to means for rotating it at a determined speed, on that of its ends which projects from the frame it supporting the wheel to be balanced.
The frame is supported on the bed via elastic means which give the frame a freedom of movement in a predetermined direction, and is associated with two force transducers which read the forces induced by the wheel imbalance when this is rotated.
So-called fixed shaft machines are also known in which the shaft is directly supported by the bed, and carries at its projecting end a rotary assembly for supporting the wheel.
Hereinafter a rotary shaft machine will be described, however that stated applies equally well to a fixed shaft machine by merely replacing the fixed shaft by the aforesaid frame.
Said two force transducers are positioned at a determined distance apart, to define the two planes perpendicular to the shaft axis in which the imbalance forces are measured.
A processor processes the values of said imbalance forces and calculates the value and the position of the balancing masses in two different planes of the wheel.
The general characteristics of balancing machines are well known to the expert of the art, hence a more detailed description thereof will be omitted. It will merely be noted here that to make the effect of the inertial forces generated by the rotating system negligible compared with the imbalance forces, the resonance frequency of the entire machine, including its rotating parts, must be much greater than the rotational speed of the shaft. The present patent relates in particular to the elastic suspensions on the frame which carries the rotary shaft.
The arrangement generally used for said suspensions comprises a pair of coplanar leaf springs positioned spaced apart and arranged to deform within the plane perpendicular to the shaft axis.
Said leaf springs lie in a plane parallel to the shaft axis, which may also sometimes contain said axis.
One of the problems which afflict known machines rises from the need to rotate the wheel to be balanced at a constant speed, without the motion transmission means influencing the balance measurement which is to be effected.
In order to nullify the influencing effect of the means which rotate the rotary assembly of the machine, solutions have been devised in which this assembly is initially rotated at a predetermined speed, but with total disengagement of the rotation means while effecting the measurement. However these solutions present subordinate drawbacks which sometimes make their use inconvenient.
A first important drawback arises from the fact that while effecting measurements the speed inevitably decreases, so negatively influencing the measurements.
A second drawback arises from the presence of disengagable couplings, the operation and construction of which are complicated and which are of high cost.
The object of this patent is to provide a balancing machine of simple and economical construction which is free of the aforesaid drawbacks.
Specifically the invention concerns a machine in which the means which rotate the moving assembly are always engaged.
The objects of the invention are attained by a balancing machine described as follows.
In detail, the balancing machine of the invention comprises a permanently engaged belt transmission and, for the moving assembly, elastic suspension means consisting of two coplanar leaf springs positioned diametrically in relation to the shell which comprises the moving assembly and lying in a plane perpendicular to the plane which connects the axis of the moving assembly to the axis of the pulley which rotates it.
The motor, on the shaft of which the drive pulley for the belt transmission is keyed, is rigid with the fixed outer shell or frame of the moving assembly.
By virtue of said configuration, under the pulling action of the belt the two leaf springs deform overall, with a deformation which passes through the axis of the moving assembly, hence their deformation does not stress the force transducers which are disposed in the plane containing the axis of the moving assembly and the axis of the drive pulley.
The different tensions, in whatever manner they vary, to which the two branches of the belt are subjected have a resultant which can be resolved into a first component passing through the axis of the drive pulley and perpendicular to the plane containing the axis of the two pulleys, i.e. the drive and driven pulley, and a second component contained in the plane containing the axes of the drive and driven pulleys.
The second component is absorbed by the rigid connection between the motor and the shell of the moving assembly, and hence does not act on the force transducers.
The first component, translated into the plane containing the axis of the moving assembly, stresses the leaf springs one in compression and one in tension in the plane in which they lie, and generates a moment which deforms the leaf springs symmetrically, with a deformation having a neutral axis passing through the axis of the moving assembly. Hence the first component does not stress the force transducers.
Any shape irregularity of the belt results in asymmetry of the tensions in the two branches which in its turn results in a force and a moment similar to the aforedefined, and hence does not influence the force transducers. In this respect, the force transducers are applied to the shell supporting the rotary assembly in the diametrical plane containing its axis and the axis of the drive pulley, and pick up only those forces due to the imbalance, the other forces all being mutually balanced or non-influential to the transducers.
The aforestated also applies if the motion transmission is by a friction roller or gearwheels.